In accordance with a rapid spread of information related to apparatuses and communication apparatuses such as a personal computer, a video camera and a portable telephone in recent years, the development of a battery to be utilized as a power source thereof has been emphasized. The development of a high-output and high-capacity battery for an electric automobile or a hybrid automobile has been advanced also in the automobile industry. A lithium battery is of interest from the viewpoint of a high energy density compared to other kinds of batteries.
A liquid electrolyte including a flammable organic solvent is used for a conventional commercial lithium battery, so that the installation of a safety device for restraining temperature rise during a short circuit and the improvement in structure for preventing the short circuit are necessary therefor. In contrast, a solid state battery such that the liquid electrolyte is replaced with a solid electrolyte layer to provide an all solid battery is conceived to simplify the safety device and improve production cost and productivity because a flammable organic solvent is not used in the battery.
Solid electrode materials (such as an active material, a solid electrolyte material, and a conductive material) form the electrode body of an all solid battery, so that the structure in which materials are adhered to each other is important. For example, Patent Literature 1 discloses a composite active material having an active material (such as LiNi1/3Mn1/3Co1/3O2), an oxide solid electrolyte layer (such as LiNbO3) that coats the active material, and a sulfide solid electrolyte layer. Patent Literature 1 also discloses a configuration where the coverage of the sulfide solid electrolyte layer is 76% or more, preferably in a range of 85% to 95%. The object of Patent Literature 1 is to decrease the reaction resistance of a battery. As for another example, Patent Literature 2 discloses a technique of forming a coating layer including a sulfide solid electrolyte material in the surface of the active material by conducting a rotation and revolution mixing treatment with respect to the raw material composition including an active material and a sulfide solid electrolyte material. As for the other example, Patent Literature 3 discloses the configuration of BET specific surface area of a composite active material in which the active material is coated with a sulfide solid electrolyte material, being less than 2.82 m2/g.